In certain solenoid-controlled valves, the solenoid is exposed to fluid whose flow is controlled by the valve. Generally speaking, it is undesirable for the fluid to come in contact with the solenoid's coil. For example, intrusion of some fluids may degrade insulation covering the wire forming the coil, and this may lead to shorting of turns of the coil, and ultimately loss of coil performance. Accordingly, it has been appropriate to adopt protective measures for guarding against such intrusion.
However, it is important that protective measures should not have a degrading effect on the magnetic circuit because it may then be necessary to enlist other measures, such as enlarging the size of the solenoid for example, and these measures may be undesirable from other standpoints, such as cost or package size for example.
The present invention relates to a novel construction for a solenoid that can keep the coil dry without detrimentally compromising the solenoid's magnet circuit. Described briefly and in a general way, the invention comprises providing the solenoid with an imperforate transverse end wall that separates the coil from the fluid and that has radially outer and radially inner annular zones of magnetic material forming respective portions of the stator separated from each other by a radially intermediate annular zone of non-magnetic material. Various constructional techniques for fabricating this end wall will be described.
A drawing accompanies the disclosure and depicts a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.